1. Technical Field
The present invention relates generally to data transmission in fiber optic ring networks, by way of example, the synchronous optical networks, (SONET networks) and Synchronous Digital Hierarchy networks (SDH networks) and more particularly, to the routing of IP data packets through the fiber optic ring networks including SONET and SDH networks.
2. Related Art
New networks and information exchange capabilities that were unimaginable even in recent times are being developed and implemented in a way that impacts businesses and individuals in a significant way. For example, standalone computers may now be integrated with wireless radio telephones to allow the transmission of information from the computer to a destination by way of a wireless communication network and then by way of the internet.
The recent explosion of the internet is creating the capability and desire for networks of all types to be integrated and coupled to exchange data signals carrying the varying types of information. In many cases, the same data also will also be transported through a local area network (LAN) prior to being delivered to the internet. Thus, by way of example, a digitized signal can be transported from a source through a LAN and through the internet, to a final destination. Moreover, within the internet portion itself, there may be a need to transport the user data through a backbone data transport infrastructure, by way of example, through a fiber optic ring network.
Generally speaking, the internet is, in essence, a collection of many large and small computer networks that are coupled together over high speed backbone data links such as T-1, T-3, OC-1 and OC-3. Stated differently, the internet is a network of networks. As a result of the creation of the internet, worldwide access may be achieved. People and their equipment may now communicate from most any civilized point to another in a fast and relatively inexpensive medium.
While it is popular to think of the internet as one network of networks, there are other such internets that are in existence and that are under development. For example, the network now commonly known as the internet was originally a network of institutional networks including university networks. As a result of the commercialization of the internet and the resultant reduction in quality of service, new generation internet type networks are under development to better achieve the purposes of the original “internet”. Moreover, new international standards and protocols are being approved to create additional and enhanced internets. For the sake of simplicity, however, each of the worldwide internet networks will be referred to collectively as the internet.
Regarding its physical aspects, the internet is a packet switched network that is currently based upon a group of protocols known as transmission control protocol/internet protocol (TCP/IP). TCP is a connection-oriented protocol that first establishes a connection between two computer systems that are to exchange data. TCP then breaks a given digital information signal into packets having a defined format. The packets are then attached to headers that are for containing control and address information.
For example, in addition to a destination address, a TCP packet typically contains a sequence number that is to be used by the destination in reconstructing a signal that is similar to the original digital information that was broken into packets at the originating end. TCP packets also typically include port IDs, checksum values and other types of control information as is known by those skilled in the art.
IP protocol is used for routing purposes. Thus, the IP protocol includes the destination and originating addresses and default gateway identifiers. IP routers, therefore, are operable to evaluate IP protocol information for routing an IP data packet and to evaluate TCP protocol information for error control and other similar purposes.
In order to make communication devices created by companies throughout the world compatible with each other to create local area networks and worldwide networks such as the internet, protocols and standards are often defined. These protocols and standards are used to guide the design of the communication devices, and more specifically, to guide the design of the operating logic and software within the devices. While communication devices that are designed in view of these standards do not always follow the suggested models exactly, they are usually compatible with the protocol-defined interfaces (physical and logical). In order to appreciate the construction and operation of many devices, it is important to generally understand the concepts of some of the significant protocol standards and models.
One important model that currently guides development efforts is the International Standards Organization (ISO) Open Systems Interconnection (OSI) model. ISO/OSI provides a network framework or model that allows equipment from different vendors to communicate with each other. The OSI model organizes the communication process into seven different categories or layers and places these layers in a sequence based on their relation to the user. Layers 1 through 3 deal provide actual network access and control. Layers 4 through 7 relate to the point to point communications between the message source and destination.
More specifically, the seven layers in the OSI model work together to transfer communication signals through a network. Layer 1 includes the physical layer meaning the actual hardware that transmits currents having a voltage representing a bit of information. Layer 1 also provides for the functional and procedural characteristics of the hardware to activate, maintain, and deactivate physical data links that transparently pass the bit stream for communication between data link entities. Layer 2 is the data link layer or the technology specific transfer layer that effectuates and controls the actual transmissions between network entities. For example, layer 2 provides for activation, maintenance, and deactivation of data link connections, character and frame synchronization, grouping of bits into characters and frames, error control, media access control and flow control.
Layer 3 is the network layer at which routing, switching and delaying decisions are made to create a path through a network. Such decisions are made in view of the network as a whole and of the available communication paths through the network. For example, decisions as to which nodes should be used to create a signal path are decided at layer 3. As may be seen, layers 1, 2 and 3 control the physical aspects of data transmission.
While the first three layers control the physical aspects of data transmission, the remaining layers relate more to communication functionality. To illustrate, layer 4 is the transport layer that defines the rules for information exchange and manages the point to point delivery of information within and between networks including providing error recovery and flow control. Layer 5 is the session layer that controls the basic communications that occur at layer 4. Layer 6 is the presentation layer that serves as a gateway (a type of “software” interface) between protocols and syntax of dissimilar systems. Layer 7 is the application layer that includes higher level functions for particular application services. Examples of layer 7 functions include file transfer, creation of virtual terminals, and remote file access.
Each of the above defined layers are as defined by the OSI model. While specific implementations may vary from what is defined above, the general principles are followed so that dissimilar devices may communicate with each other.
With respect to the forgoing discussion regarding the seven OSI layers, IP is a layer three protocol. In contrast, many of the backbone data transport infrastructures utilize a different layer protocol than an internet router.
Many of the common backbone data transport systems utilized include time division multiplexed (TDM) double ring transmission systems. Double ring TDM systems are generally known, especially for fiber-optic communication networks. In order to maintain transmission in the event of a fault on one of the channels or communication links, it is typically common to find ring transmission systems in which transmissions occur in two directions. Specifically, transmissions occur in one direction through all of the nodes in the ring in a working path and through an opposite direction in a protection path. The protection path is, traditionally, a redundant path for transmitting signals in a failure condition. Examples of fiber optic TDM systems include the SONET and SDH double ring fiber optic communication systems used in North America and Europe, respectively.
In ordinary conditions, either the user traffic (data) in the redundant path in these double ring systems is not routed through the protection path or, alternatively, it is routed but is not processed by a destination. At the same time, its communication channels are reserved as an alternate path during failure conditions. The redundant path is typically used to route the data signals in an opposite direction from the working path so that data that is to be routed to a destination node located, “downstream” from the failure condition may still be delivered to the destination node.
One problem with this approach, however, is that the capacity of the redundant ring must be reserved as a redundant path. Transmission efficiency and throughput capacity must be sacrificed to provide data protection. Additionally, error conditions that prompt a node to switch to the protection path often are related to hardware (layer 1) problems in which communications are not being successfully transmitted in a communication link. Switching does not occur for those conditions in which switching may be desirable even if there is not a hardware related error. For example, switching might be desirable to alleviate user traffic congestion.
Additionally, several challenges exist in implementing dual ring topologies. For example, it is necessary for the switching from the working path to the protection path to occur quickly in the event of a fault so that a minimal amount of information is lost. Typically, switching occurs at the layer 1 level to minimize the down time. As a result, however, little error protection is provided at the hardware level for failures. Additionally, layer 1 switching results in the switching of entire data transport pipelines.
To accomplish fast switching, layer 1 overhead signaling messages are generated and transmitted back to the ingress node (among other nodes) identifying the fault condition so that the protection switching may occur quickly. More specifically, layer 1 overhead signaling messages are transmitted by the nodes detecting the error (typically the two nodes on either traffic side of the detected problem) on a communication link so that the ingress node may effectuate the change on a quick basis. Typically, the ingress node includes dedicated circuitry for reading, interpreting and quickly responding to the overhead signaling message to effectuate a change. As is implied by the foregoing discussion, the overhead signaling is set upon the occurrence of a significant hardware failure in a communication link.
Historically, delays that are encountered in the internet have been acceptable, though not well liked, in the context of computer to computer communications. As other types of data are transported over the internet, by way of example, either voice or video, there will be a need for transporting data in large quantities in a quick manner. Due to this reason, failure recovery should be fast. There is, therefore, an increasing need for integrating internet communication networks with fiber optic ring networks utilizing a TDM protocol for transporting data because of the speed and throughput capacity of fiber optic ring networks. Accordingly, there is a need for a fiber optic ring network node that is capable of reliably and quickly transporting user traffic to and from the internet.